福建九龙江河口第四纪沉积物特征及沉积环境演变

根据福建九龙江河口ZK1孔及ZK7孔沉积物AMS(Accelerator Mass Spectrometry,加速器质谱测年技术) ¹⁴C测年、古地磁和剖面特征分析,进行该地区的第四纪地层划分,依据粒度特征,结合磁化率、微体古生物和Sr/Ba等环境代用指标进行沉积相分析,重建了该区晚第四纪的古环境演变历史。结果表明:(1)九龙江河口第四纪沉积时代为晚更新世中期至全新世晚期。(2)上更新统沉积可划分为下部龙海组洪冲积相和上部东山组河漫滩相沉积,中间有10 ka的沉积间断,末次冰期又再遭受风化剥蚀作用,推测有5～6 ka的风化剥蚀期。(3)全新统最早沉积年代约为14 ka BP,依次出现河口湾相、河口砂坝—分汊河道相、潮滩相沉积。(4)根据年代学数据和沉积相变化,重塑了该区晚第四纪沉积环境变化过程,为该区的第四纪研究和工程地质工作提供了参考依据。

Sedimentary characteristics and depositional environmental evolutionof the Quaternary in Jiulongjiang Estuary,Fujian Province

Based on the analysis of AMS¹⁴C dating and palaeomagnetic data,combined with the section characteristics of Boreholes ZK1 and ZK7 located in Jiulongjiang Estuary,the Quaternary are subdivided in the area. According to mainly granulometic characteristics,associated with other palaeoenvironmental indexes such as magnetic susceptibility,micropalaeobios,ratio of Sr/Ba etc.,the sedimentary facies are defined to restore the history of palaeoenvironmental evolution during the Late Quaternary. It indicates that the quaternary sediments of Jiulongjiang Estuary formed from middle of the Late Pleistocene to the Late Holocene. The sediments of the Late Pleistocene can be subdivided,from bottom to top,to Longhai Formation(flood-alluvial facies)and Dongshan Formation(flood plain facies),intermitted by a depositional breaks of about 10 ka. During the last glacial period,these sediments were exposed to suffer weathering and erosion for about 5～6 ka. The sediments of the Holocene,formed from 14 ka BP,is defined as Changle Formation consisting successively of estuarine facies,distributary mouth bar-channel facies and tidal-flat facies. According to the dating data and the changes of sedimentary facies,the process of evolu￣tion is restored for the Late Quaternary palaeoenvironment in this area,and the results of this study may provide basic information for the regional Quaternary and engineering geologic researches.